The day after Nightmare Night, Princess Celestia unexpectedly visits Twilight at her library. She scolds Twilight, accusing her of forcing Luna to relive the worst time of her life by taking on the guise of Nightmare Moon.
Luna is close behind her sister, and she and Twilight have a heart-to-heart conversation wherein each comes to understand the other a bit better.
This story takes place shortly after the events of Luna Eclipsed.